Engines may utilize a turbocharger or supercharger to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point temperature. Further, when the charge air entering the CAC is boosted (e.g., an induction pressure and boost pressure are greater than atmospheric pressure), condensate may form if the CAC temperature falls below the dew point temperature. As a result, condensate may collect at the bottom of the CAC, or in the internal passages of the CAC. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire and combustion instability.
Other attempts to address engine misfire due to condensate ingestion involve avoiding condensate build-up. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. Another method to prevent engine misfire due to condensate ingestion includes trapping and/or draining the condensate from the CAC. While this may reduce condensate levels in the CAC, condensate is moved to an alternate location or reservoir, which may be subject to other condensate problems such as freezing and corrosion.
Condensate build-up in the CAC may also be addressed by removing condensate from the CAC before it builds up to a threshold level by increasing airflow through the CAC. For example, as shown in 2014/0048048, adjusting a valve positioned in an inlet tank of a variable volume CAC may adjust the airflow rate through the CAC. Increased airflow through the CAC may reduce condensate build-up in the CAC. However, the inventors herein have recognized potential issues with such systems. As one example, a variable volume CAC may require additional parts and controls for controlling airflow through the CAC.
In one example, the issues described above may be addressed by a method for transiently increasing airflow through a charge air cooler (CAC) of the engine by one or more of operating in a VDE mode or opening a compressor bypass valve (CBV) and maintaining engine torque by increasing boost pressure. In this way, the increased airflow may purge condensate from the CAC and reduce engine misfire events and/or unstable combustion due to ingestion of large amounts of condensate by the engine.
As one example, an engine controller may increase airflow through the CAC by one or more of operating the engine in the VDE mode or opening the CBV while increasing boost to maintain torque in response to a condensate level of the CAC increasing above a threshold level. In one example, operating in the VDE mode includes selectively deactivating a number of engine cylinders, the number of engine cylinders based on the condensate level. The selectively deactivating the number of engine cylinders includes deactivating fueling to the deactivated cylinders while maintaining intake and exhaust valve operation. In another example, the CBV may be arranged in a bypass passage positioned between an intake passage downstream of the CAC and the intake passage upstream of a compressor. As such, opening the CBV recirculates air around the CAC and the compressor, thereby increasing airflow through the CAC. In an alternate example, the increasing CAC airflow may be performed periodically at set intervals. In this way, condensate build-up may be reduced, thereby reducing engine misfire events.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.